1. Field of the Invention
The present invention relates to a wiring layout structure in an optical head device for reading and/or writing signals on a signal recording medium by means of a laser beam irradiated from a laser source.
2. Description of the Related Art
In a typical optical head device, an actuator for driving an objective lens is mounted on an optical housing. Various optical components other than the objective lens are also assembled on the optical housing. The optical head device comprises a semiconductor laser which serves as the light source, a photodetector for receiving laser light which has been reflected off of a signal recording medium, and a semiconductor integrated circuit for driving the semiconductor laser. The optical head device further includes electrical components such as a coil, a capacitor, a resistor for setting a circuit constant and a front monitor diode for receiving and monitoring the laser beam irradiated from the semiconductor laser so as to maintain the amount of light output from the laser at a predetermined level.
The actuator for driving the objective lens is composed of a permanent magnet, yoke, and various drive coils (focus coil and tracking coil, along with a tilt coil when necessary). Drive signals are supplied to the various drive coils.
In the optical head device, a flexible wiring board is employed to interconnect the electrical components provided in the optical head device and to supply drive signals to the various drive coils. The flexible wiring board generally comprises FPC (Flexible Printed Circuit).
Positions of the electrical components provided in the optical head device and positions of the terminals for supplying drive signals to the various drive coils are determined while taking into account the optical arrangement, connection relationships among the electrical components, and the position of the actuator. In addition, a desirable arrangement of the components may be devised by folding the flexible wiring board. As a result, the designed shape of the flexible wiring board is often complex, with branched portions.
The front monitor diode must be arranged within a branch light path formed by branching from the light path extending from the laser source to the signal recording medium. Accordingly, a signal path portion formed on the flexible wiring board for connecting to the front monitor diode is generally arranged in a central portion of the optical head device. The signal path portion for connecting to the front monitor diode may be positioned on an upper surface of the optical housing at a portion at which the actuator is mounted.
Further, the signal path portion formed on the flexible wiring board for connecting to a relay portion which relays drive signals to be supplied to the respective drive coils of the actuator is generally arranged adjacent to the portion of the optical housing at which the actuator is mounted.
As described above, the signal path portion for connecting to the front monitor diode and the signal path portion for connecting to the relay portion, which are both formed on the flexible wiring board, a repositioned adjacent to the actuator. The flexible wiring board may be held in position while being bent along the contour of the optical head device. Because of the restorative force of the flexible wiring board generated at a bent portion, there exists a risk that the signal path portions which are formed on the flexible wiring board and positioned adjacent to the actuator inadvertently contact the movable components of the actuator including the objective lens holder and a support member (such as a suspension wire) for supporting the lens holder while enabling displacement of the lens holder.
Moreover, because the signal path portion for connecting to the front monitor diode and the signal path portion for connecting to the relay portion are located close to one another, the conventional configuration described above results in a crowded arrangement of the signal path portions.